Dieback of pine stands in Eastern Polissya: distribution, consequences, measures to overcome

Abstract

The features of the spread of pine stands decline in the Eastern Polissya of Ukraine under biotic and abiotic factors impact are generalized and highlighted. The works were carried out according to the generally accepted methods of forest pathological and forestry-taxation research on the forest pathological routes in pine stands with signs of tree decline and in foci of tree mortality, at the permanent and temporary plots in the dieback foci. To determine the species composition, population indices, and population density of stem insects in the dieback foci, periodic decadal assessments were carried out in the exposed pheromone traps and in different parts of the stem of model trees according to entomological research methods. It is determined that the drying of pine trees in previous years was mainly due to damage of trees by the pathogen of the root rot Heterobasidion annosum (Fries) Bref. At the beginning of the growing season in 2015 the reconnaissance surveys revealed the spread of pathological drying of pine stands. After periodic prolonged droughts during the vegetation periods of 2015–2017, in the following years, the intensity of the group formation , curtain dieback foci increased with a tendency to continuous drying of pine stands. Mainly pines of middle-aged and older age, artificial origin, pure composition, simple form, less stand density in all types of forests dried. Dieback foci initially appeared near the forest edge, narrow strips and low-density pine stands, moving to other pines from the south-western to the north-eastern part of Eastern Polissya. Area of pine stands with dieback foci in the study region annually amounted to 12.5–17.1 thousand ha (6–8% of their total area). Based on detailed forest pathological inspection, it was found that tree weakening and the dieback of stands occurred due to the mass propagation of stem insects – Ips acuminatus Gyll. and Ips sexdentatus Boern. It was determined that the population density of the young generation of Ips acuminatus during 2017–2018 exceeded the average population indices by 10 or more times with production up to 100 juvenile beetles per dm2 of populated stem area. The possibility of three generations of Ips acuminatus development per year under favorable conditions has been revealed. Due to unfavorable weather conditions for wintering of stem insects and exceeding the long-term precipitation with a decrease in temperature at the beginning of the growing season in 2019 the density of bark beetle populations decreased significantly (2–3 times) with the formation of only single and group dieback foci. The number of insects decreased due to the restoration of water supply to pine trees, which made it possible to maintain sufficient resin release and flooding of mother and larval galleries with adult beetles. With sufficient moisture, pine trees of the 1st-2nd categories of health condition are able to maintain a stable level of resin productivity for a long time compared to weakened trees. Therefore, it is important to reproduce more resistant pine stands of mixed composition, natural origin, complex shape structure. For the first time, it has been found that very weakened and drying up pine trees are able to rapidly but briefly release more resin than more viable trees. To reduce and overcome the effects of pine forests dieback, a set of forestry and protective measures should be applied: sanitary felling, attraction of birds and other entomophagous animals, application of mineral fertilizers, and stem injections of the most valuable trees.

Keywords

• tree decline; stem pests; categories of tree health condition; sanitary felling.